Design And Application Of Surface Plasmon Resonance Sensor Based On Nanoparticles Amplification

The sensor based on surface plasmon resonance (SPR) is an advanced means for biomolecular interaction analysis. Compared to other technologies, SPR has many advantages such as high sensitivity, label-free, real-time detection, convenience, fast and less sample volume requirement. SPR biosensors have attracted increasing attention and have been widely used in various fields including environmental monitoring, food safety, biomedical and drug screening. However, one of the main drawbacks of SPR biosensors is that the SPR system has insufficient sensitivity to detect small molecules or low-concentration compounds at the sensing surface, because the binding of such analytes causes only a small change in the refractive index of the medium. It is a major factor for limiting the application of SPR sensor, therefore, several approaches commit to the development of sensitivity enhancements for SPR biosensors. In this work, the theory, technical characteristics, application of SPR biosensor are introduced. The gold nanoparticles and magnetic nanoparticles are introduced into SPR sensor, and we combine with other detection technique (such as molecular imprinting technology, aptamer technology, DNA amplification technology) to improve the performance of SPR biosensor. In detail, the thesis includes the following parts:1. In this work, we have demonstrated a sensitive SPR sensing protocol based on magnetic surface imprinting technique for the detection of organophosphate pesticide for the first time. The core-shell imprinted Fe3O4@PDA NPs are prepared by a facile approach based on self-polymerization of dopamine in the presence of template CPF on the Fe3O4NPs surface. The obtained core-shell imprinted Fe3O4@PDA NPs sphere nanostructures shows the excellent magnetic properties of Fe3O4core, allowing for the direct capture and easy separation and concentration of targets in complex samples in an external magnetic field. And the high surface-to-volume ratios of Fe3O4NPs, allowing for increasing the number and ratio of imprinted sites that are accessible for binding, and therefore binding capacity of the MIPs. In addition, the controllable membrane-forming ability of PDA shell facilitates the situation of the imprinted sites on the surface of Fe3O4NPs, which can provide fast association/dissociation kinetics for template recognition. Therefore, sensitive and selective detection of CPF have been achieved by employing the imprinted Fe3O4@PDA as both an amplifier to increase the SPR signal and a special recognition element to improve the selectivity due to its high refractive indices, high molecular weights and imprinted effect, and detection limit of the sensor is0.76nM. Compared with the traditional pesticide detection technology, the detection technology based on magnetic surface imprinting technique has a good application prospects.2. Aptamers are nucleic acids that show high affinity and selectivity for their target molecules. Here, we combine the advantage of aptamer technique with the amplifying effect of strand displacement cycle and Au nanoparticles (NPs) to design a sensitive SPR aptasensor for detecting small molecules. Our detection system consists of adenosine aptamer, detection probe (c-DNA1) that partially hybridizes to the aptamer strand, Au NPs-linked hairpin DNA (Au-H-DNA1), and thiolated hairpin DNA (H-DNA2) that is first immobilized on SPR gold chip. In the absence of adenosine, the H-DNA1possessing hairpin structure could not hybridize with H-DNA2and thereby Au NPs could not be captured on SPR gold chip surface. However, in the presence of adenosine, the c-DNA1dissociates from the H-DNA1/H-DNA2complex due to the high affinity of aptamer and then c-DNAl can facilitate the opening of the hairpin structure of Au-H-DNA1and thus accelerate the hybridization between H-DNA1and H-DNA2and ultimately releasing the c-DNA1which initiate a new cycle. In this way, a single target can trigger many Au-H-DNAl to assemble on the SPR gold film, resulting in a huge SPR signal due to the amplification effect of Au NPs. By monitoring the change in SPR angle, we could detect the target with high sensitivity. The detection limit of this SPR aptasensor is0.21pM, which is more than3orders of magnitude lower than that of the SPR aptasensors based on only strand displacement cycle or Au NPs amplification. Furthermore, this amplified aptasensor shows high selectivity toward its target. In addition, this approach does not require expensive protein enzymes and complicate thermal-cycling procedures. Thus, the proposed SPR aptasensor could be used as a simple, sensitive and selective platform for target molecules detection. In particular, this is the first develop amplified SPR biosensing based on aptamer technique combined with Au NPs and DNA cycle-amplifying technique, which has greater potential in bioassay applications.